1. Field of the Invention
The present invention relates to an internal gear pump that can improve volume efficiency.
2. Description of the Related Art
Conventionally, there is an internal gear pump including an inner rotor and an outer rotor. Concerning tooth profiles of the inner rotor and the outer rotor, various researches and developments have been conducted and inventions for improving pump efficiency have been devised. As such inventions, there are Japanese Patent Application Laid-open No. S55-148992 and WO2008/111270.
In Japanese Patent Application Laid-open No. S55-148992, teeth of an inner rotor start to push (or start to mesh with) teeth of an outer rotor in a deepest meshing section. Consequently, force is applied to the outer rotor from the deepest meshing section to a front side in a rotating direction of the rotors. In other words, force in a direction substantially lateral to a conveying side, which is a maximum cell volume section, is applied to the outer rotor.
In an oil pump rotor in WO2008/111270, outer tooth profile shapes (U1in, U2in) of a patented inner rotor are formed by deformation in the circumferential direction (U1, U2) and deformation in the radial direction (U1in, U2in) applied to tooth profile shapes (U′1, U′2) formed by mathematical curves while maintaining a distance between a radius (RA1) of a tooth tip circle (A1) and a radius (RA2) of a tooth groove circle (A2).
A region where the teeth of the inner rotor and the teeth of the outer rotor mesh with each other is calculated on the basis of the tooth profile shapes of the inner rotor 10 and the outer rotor 20. For example, in an example of an oil pump shown in FIG. 10 disclosed in WO2008/111270, a curve between a tooth groove side meshing point “b” and a tooth tip side meshing point “a” is a region where the inner rotor 10 and the outer rotor 20 mesh with each other.
In other words, when the inner rotor 10 rotates, in outer teeth 11a of the inner rotor 10, the inner rotor 10 and the outer rotor 20 start to mesh with each other at the tooth groove side meshing point “b” (see FIG. 10A of WO2008/111270). Thereafter, the meshing point gradually slides to the tooth tip side of the outer teeth 11a. Finally, the inner rotor 10 and the outer rotor 20 fail to mesh with each other at the tooth tip side meshing point “a” (see FIG. 10B of WO2008/111270).
As explained above, in WO2008/111270, the inner rotor and the outer rotor start to mesh with each other further on a negative side in the rotating direction of the rotors than the deepest meshing section and fail to mesh with each other further on a positive side in the rotating direction of the rotors than the deepest meshing section. Consequently, force is applied to the outer rotor on the front side in the rotating direction of the rotors from the deepest meshing section. The force is force in a direction substantially lateral to a conveyance side, which is a maximum cell volume section.
In Japanese Patent Application Laid-open No. S55-148992, in a trochoid rotor, the inner rotor and the outer rotor start to mesh with each other in the deepest meshing section. Consequently, force is applied to the outer rotor on the front side in the rotating direction of the rotors from the deepest meshing section. The force is applied from the inner rotor to the outer rotor is force in a direction lateral to the conveyance side, which the maximum cell volume section. Therefore, the force is not force in a direction in which a tip clearance on the conveyance side decreases. Therefore, the tip clearance on the conveyance side does not decrease and a leak does not decrease. Therefore, volume efficiency is not improved.
In WO2008/111270, the inner rotor and the outer rotor start to mesh with each other further in a negative position in the rotating direction than the deepest meshing section and finish meshing with each other in a positive position in the rotating direction.
When the deepest meshing section is set as zero, a meshing range extends from the negative side in the rotating direction to the positive side in the rotating direction. As a result, the force applied from the inner rotor to the outer rotor is force in the direction lateral to the conveyance side, which is the maximum cell volume section. The force is not force in the direction in which the tip clearance on the conveyance side decreases. Therefore, the tip clearance on the conveyance side does not decrease and a leak does not decrease. Therefore, volume efficiency is not improved.